Trade Secrets

Motor, Mar 2005 by Cerullo, Bob

Keeping up with new technology makes good business sense. But when that technology includes the high voltages in gas/ electric hybrid systems, it also makes good safety sense.

A good friend of mine-a top technician-attended a training course on gas/electric hybrids recently and came away with the distinct impression that it was a bit too easy to be electrocuted while working on a hybrid vehicle. He mimicked the trainer when he said: "If you touch the orange wires, YOU WILL DIE. If you do not discharge the capacitor before touching it, YOU WILL DIE. If you fail to check the voltage in the high-voltage circuits, YOU WILL DIE." Those are pretty ominous warnings, even if they're exaggerated to make a point. Which brings up a good question: What is the risk when working on a hybrid vehicle?

The possibility of being electrocuted by a jolt from a 144- to 500-volt hybrid electrical system seems to have been raised when tow truck operators and rescue workers were alerted to the fact that hybrid vehicles contain high-voltage circuits. Toyota placed advertisements in trade publications and sent letters to industry organizations announcing the availability of guidelines for dealing with the high voltages on its hybrid vehicles. This led to warnings from towingrelated magazines and from at least one tow truck operators association. What started as a legitimate warning to firefighters, EMTs and wrecker operators has snowballed into what Wade Hoyt, Toyota's Northeast Public Relations Manager, calls "urban legend."

Fuel was added to the Are (pardon the pun) when USA Today addressed the subject in a story titled "Shock prevention for hybrids." On January 26, 2004, the Los Angeles County Sheriffs Dept. issued a Safety Bulletin that specifically mentioned a firefighter from Montgomery County, Maryland, who "noticed something strange" when he approached a wrecked car, which turned out to be a hybrid. "The engine appeared to be off and the injured driver had her foot on the brake. The firefighter was unaware the engine was still running on silent electric power and could have surged iorward, hitting rescuers or bystanders." Actually, the car did not surge forward and there's no mention of the firehghter receiving any electrical shocks. But the key phrase here is "could have."

The fact is that high voltages like the 275-volt NiMH battery pack in the Prius-and similar batteries in other hybrids-do have the potential to kill. But then again, consider the explosive power of the gasoline stored in the fuel tank of every internal combustion engine vehicle on the road.

More and more makes and models of hybrids will be appearing on the roads in the near future. Among the carmakers who are either planning to build hybrids or who are planning additional models of current hybrids are Ford, Honda, Toyota, General Motors and Daimler-Chrysler. That means many models that were originally conventional internal combustion vehicles will be offered in hybrid form as well, and confusion is inevitable-especially in an emergency situation. First rcsponders are calling for a warning label-possibly on the sun visor-that would alert them to the fact that a particular vehicle is a hybrid. They would like to have a simple, universal way to safely shut down all power from the engine compartment.

In the case of the Toyota Prius gas/electric hybrid, for example, the high-voltage batteries are contained in strong steel case located in a portion of the vehicle unlikely to he penetrated in a collision. Drivetrain management computers that continuously monitor all system functions perform hundreds of tests each minute. In the event an abnormal condition is detected, all high-voltage circuits are disabled and the voltage is contained inside the protective case. In addition, there are two safety mechanisms that will shut off the engine and disconnect the high-voltage circuits if an air bag accidentally deploys or if there's a sudden deceleration, as would occur in an accident. That does not mean that you, as an automotive repairer, still can't do something foolish and get hurt.

Before you poke around in any of the high-voltage areas of a hybrid vehicle, you need to know the colors that signify a potential electrical hazard for that vehicle. If you're colorblind, you better have an assistant there to help you.

But there's much more to know than simply not to touch anything orange, and that requires specific training for each model. On the Honda Insight, for example, be sure the 144volt system is not hot before you touch anytliing. You can drain the capacitors by removing the rear deck carpet and the two-bolt access panel. Remove the red switch cover and turn off the switch. Reinstall the cover, then wait at least five minutes. Check the orange cable for low voltage using a voltmeter. If the voltage is 12 volts or less, you can safely work on the car. If voltage is more than 12 volts, (ind out why you haven t successfully drained the capacitors.

When powering down the Prius, Toyota suggests using rubber gloves when working around high voltage. Rubber-soled shoes and a rubber floor mat might be a good idea, too. Make sure you're not standing on a wet floor, and don't even think of washing the engine with water. Never work on the car with the ignition on. But most important of all, wear your thinking cap and learn the safety precautions before you dig in, because they're not something that will come simply from common sense. You need to read the manuals on these hybrid vehicles and understand them.